-----Original Message-----
From: Bruno Marchal <[EMAIL PROTECTED]>
Cc: everything-list@eskimo.com
Sent: Sat, 27 Aug 2005 14:31:08 +0200
Subject: Re: subjective reality

>I do think so. See Deutsch book which make clear that the MWI is based on comp. But it is explicit in Everett and in Wheeler >assessment. From a strict logical point of view, ad hoc non comp theory of MWI can be built but it is really out of topic.

> That may be Deutsch's opinion (though, again, I doubt he says anything like that in his book) but I have read both > Everett's thesis and both Wheeler's and DeWitt's defenses of it and in no way shape or form does anything like YD
>even figure in them!!!

Literally, of course. YD is just a tools for explaining what it is "to be like an Everett memory machine". It is implicit in reducing the quantum uncertainty to the ignorance of which branch we are in a superposition. Mathematically it can be justified by Gleason theorem or by Graham Hartle type of infinite "frequency" operator. See the Preskill's course on quantum computation which makes a nice summary.

I don't quite know what you mean by an "Everett memory machine" neither could I find a definition (or a mention of it) in Preskill's lectures. If by this you mean something like a machine whose memory would track the successive branchings such thing is innimical to the Everett notion that all information contained in the universal wave function is relative and all probabilities are conditional. Otherwise all "memory machines" are either (1) classical and thus relativised to one branch or (2) quantal and permanently standing in a superposition of branches so that their memories would be as "un situated" as that of any other subject. As for your "justification" I will just quote Preskill on a piece of credo which is characteristic of Many-Worlders:

"My own view is that the Everett Interpretation of quantum theory provides a satisfying explanation of measurement and of the origin of randomness, but does not yet fully explain the quantum mechanical rules for computing probabilities. A full explanation should go beyond the frequency interpretation of probability --- ideally it would place the Bayesian view of
probability on a secure objective foundation."

Though this is highly disputable in itself I think it shows quite well where your statement above is mistaken.

> Let me understand this: your aim is to derive QM from an hypothesis which, you know, is contradicted by QM ?!!!? Wow!

>I have already answered.

That is a Yes, than.

The current aim is to derive SWE (by which I mean the correct geometrical-gravity extension of Schroedinger Wave Equation) from comp. I don't expect to derive anything like SWE + collapse (although this is not entirely excluded!).
What I have already proved is that
1) if you make the move from "SWE + collapse" to "SWE + comp", then from purely arithmetical reasons you are forced to go the the quite simpler theory "comp". This is the result of the UDA reasoning and you are invited to criticize it: it presuppose some "folk-psychology" and some passive understanding of Church thesis. See the slide of my 2004 SANE paper for a presentation is eight steps. 2) I translate that reasoning into the language of a large class of universal machine and got more constructive description of the physics you need (by "1)") to derive from comp. This is technically more involved. It suppresses the need of the folk psychology.


I decrypt the above as a statement that you are NOT trying to derive QM but a more general TOE, so that assuming YD is no different than say, assuming subplankian determinism like 't Hooft or Hiley do. I guess you need a lot more good luck than I first wished you!

Because you referred me to Deutsch's book I too a look at his own defense of the Everett interpretation and was reminded also of his not so passive understanding of the CT. As it turns out his whole masterplan hinges on his belief that *CT is a result of
Physics* so he is really no great help to you.

Best regards,


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